高功率電子應用之三族氮化物於矽基板的磊晶成長與特性分析

Abstract

由於氮化鎵具備獨特的材料性質，使氮化鎵元件有優越的高崩潰電壓及高電流等特性。氮化鎵與大尺寸矽基板的整合，更使得矽基氮化鎵成為次世代高功率元件的最佳選擇。隨著矽基氮化鎵的商品化，全球高功率元件的市場更穩定成長，為提升元件之效能並進一步滿足此龐大市場需求，近年來的研究，更分別從磊晶成長及元件製作來提升元件崩潰電壓。 本論文將探討三族氮化物於矽基板的磊晶成長技術，透過有機金屬化學氣相沉積系統，發展高崩潰電壓的磊晶結構，並藉由材料分析及元件特性交互驗證磊晶品質。 第一部分，建立多重氮化鋁鎵緩衝層結構，以降低氮化鎵的差排密度，在1.2微米的氮化鎵磊晶層中，螺旋差排與刃差排密度分別為3.2×108 與 9.7×108 cm-2。其次，再藉由此多重氮化鋁鎵緩衝層的調變及圖樣化矽基板的應用，實現2.2微米無裂痕氮化鎵於矽基板上的成長，可大幅降低31%的薄膜應力，並將此結構運用在大尺寸圖樣化矽基板上，成功展示了第一顆在圖樣化矽基板上的功率元件，此元件崩潰電壓可達150伏特。 第二部分，針對氮化鋁鎵/氮化鎵/氮化鋁鎵雙異質接面場效電晶體的磊晶結構進行研究，藉由具更高崩潰電場及更高能帶的氮化鋁鎵阻障層來降低漏電流，與傳統氮化鋁鎵/氮化鎵單異質接面場效電晶體結構相比，元件崩潰電壓可從130伏特提升到超過200伏特。此外，更首創以低溫氮化鋁鎵插入層成長雙異質接面結構於矽基板上，並藉此驗證應力釋放、差排密度降低及崩潰電壓提升等特性，與傳統結構相比，崩潰電壓可提升至600伏特。此一創新磊晶結構，結合了低溫氮化鋁鎵插入層及雙異質接面磊晶結構的優點，提供了高功率元件所需的磊晶結構。

Owing to the distinctive material properties of GaN, GaN-based device exhibits superior characteristics on high breakdown voltage and high current. The integration of GaN and a large diameter Si substrate makes the GaN-on-Si device be a promising candidate for next-generation high-power applications. A global market of GaN-on-Si power electronics is steadily growing up through the commercialization of GaN-on-Si. To enhance device performances and further to meet the market demand, recent studies are focusing on the epitaxy growth and device fabrication to improve the breakdown voltage.

This dissertation concentrates on the epitaxy growth technology of III-nitride on Si substrates by using metal organic chemical vapor deposition systems and the development of epitaxial structure with high breakdown voltage. The epitaxial quality is confirmed by the material analysis techniques and the device characterizations.

In the first part, the multi-AlGaN buffer layer structure was used to reduce the dislocation density in GaN film. The screw and edge dislocation densities in the 1.2-μm-thick GaN film were 3.2×108 and 9.7×108 cm-2, respectively. Then the 2.2-μm-thick crack-free GaN films were obtained by patterning Si substrates and optimizing the multi-AlGaN layers. A 31% reduction of tensile stress for the GaN film was obtained. The first GaN power device fabricated on the large patterned Si substrate was successfully demonstrated. The breakdown voltage of the device was measured over 150 V.

In the second part, a comprehensive study of AlGaN/GaN/AlGaN double heterostructure field effect transistor epitaxial structure was investigated. A high breakdown field and high bandgap AlGaN back barrier was used to prevent the leakage current. Compared with AlGaN/GaN single heterostructure field effect transistor structure, the device breakdown voltage can be improved from 130 V to higher than 200 V. Furthermore, a novel Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double heterostructure grown on a Si substrate with the insertion of a LT-AlGaN interlayer was demonstrated. The effects of the LT-AlGaN interlayer on stress relaxation, dislocation reduction, and breakdown voltage enhancement were investigated. Compared with the traditional structures, the buffer breakdown voltage can be much improved to 600 V. By combining the advantages of the LT-AlGaN interlayer and double heterostructure, the innovation structure is an alternative epitaxial structure for high-power applications.